Magnetic resonance imaging (MRI) is a technology where the phenomenon of magnetic resonance is utilized for the purpose of imaging. The main principles of magnetic resonance are as follows. When an atomic nucleus contains a single proton, as is the case, for example, with the nuclei of the hydrogen atoms that are present throughout the human body, this proton exhibits spin motion and resembles a small magnet. The spin axes of these small magnets lack a definite pattern, and if an external magnetic field is applied, the small magnets will be rearranged according to the magnetic force lines of the external field (e.g., the small magnets will line up in two directions), either parallel or anti-parallel (perpendicular) to the magnetic force lines of the external magnetic field. The direction parallel to the magnetic force lines of the external magnetic field is the positive longitudinal axis, while the direction anti-parallel (e.g., perpendicular) to the magnetic force lines of the external magnetic field is the negative longitudinal axis. The atomic nuclei only have a longitudinal magnetization component that has both a direction and a magnitude. A radio frequency (RF) pulse of a specific frequency is used to excite the atomic nuclei in the external magnetic field such that spin axes of the atomic nuclei deviate from the positive longitudinal axis or negative longitudinal axis, giving rise to resonance, the phenomenon of magnetic resonance. Once the spin axes of the excited atomic nuclei have deviated from the positive or negative longitudinal axis, the atomic nuclei have a transverse magnetization component.
Once emission of the RF pulse has ended, the excited atomic nucleus emits an echo signal, gradually releasing the absorbed energy in the form of electromagnetic waves, such that phase and energy level both return to the pre-excitation state. An image may be reconstructed by subjecting the echo signal emitted by atomic nuclei to further processing (e.g., spatial encoding).
RF phased array coils are a type of RF receiving coil that are commonly used in MRI systems. RF phased array coils include multiple coil units (e.g., surface coil units). Inductive coupling will exist between any two coil units (e.g., surface coil units) that are close to each other, and inductive coupling will give rise to noise. In order to reduce noise and increase the reception signal-to-noise ratio (SNR) of the RF receiving coils, the inductive coupling between surface coil units is to be reduced (e.g., decouple the surface coil units).
In the prior art, common decoupling methods may include inductive decoupling, capacitive decoupling, decoupling by superposition, and low-noise preamplifer decoupling. Inductive decoupling is achieved by connecting inductively coupled coil units to a decoupling inductor assembly separately to eliminate the inductive coupling. Decoupling inductor assemblies in the prior art may include two solenoids formed by two helically wound inductive coils. The winding may consist of interwoven helixes (e.g., the inductive coils of the two solenoids are interwoven and overlapped) or adjacent helixes (e.g., the entire inductive coils of the two solenoids are positioned one above the other), with the internal areas of the two solenoids being fully or partially overlapped. When inductive decoupling is employed, the coupling inductance is to be varied by adjusting the cross-sectional area, number of turns, and winding density of the inductive coils.
For example, Chinese Patent Application Publication Number CN 102288930 A describes a magnetic resonance RF receiving coil and an inductive decoupling device thereof in the prior art.